Structural and Magnetic Properties of MgxSrxMnxCo1-3xFe2O4 Nanoparticle ferrites Nadir S. E. Oman School of Chemistry and Physics, University of KwaZulu-Natal, Westville campus, P/Bag X5400, Durban 4000, South Africa BE SURE TO READ THE NOTES !

Outline Introduction Structure and properties of spinel ferrite Synthesis and XRD measurements of the series HRTEM & HRSEM analysis Mössbauer spectroscopy measurements VSM measurement Conclusions

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Spinel Ferrite Structure Ferrite have different crystal types namely: (a) Spinel ferrite (b) Garent (c) Magnetoplumbite AB2O4 Normal spinel and inverse spinel (M2+δFe3+1-δ)[M2+1-δ Fe3+1+δ]O4 Fig. 1

Synthesis and X-ray powder diffraction (XRD) of MgxSrxMnxCo1-3xFe2O4 Glycol – thermal method was used for the synthesis of the nanoferrites. XRD patterns indicate single phase structures were formed. The lattice parameters were calculated using Bragg’s law and the equation a = d * (h2 + k2 + l2)(1/2) ρ = 8 * M / NA a3 Crystallite size were estimate using Scherer’s equation

XRD results Fig. 2

Structural parameters x a (Å) ±0.003 DXRD (nm) ±0.01 DHRTEM (nm) ±1.69 ρXRD(g/cm3) 0.001 0.0 8.380 8.27 8.55 5.30 0.1 8.387 7.91 8.33 5.26 0.2 8.34 8.66 5.24 0.3 8.379 7.28 7.42 5.23 0.33 8.395 7.20 7.83 5.18 Table 1

High- resolution electron microscopy and scanning electron microscopy measurements Typically HRTEM micrograph images at different scales. The images show the crystalline and particles distribution of the series. The crystallite size values endorsed the ones from XRD measurements. x = 0 x = 0.1 x = 0.2 x = 0.3 x = 0.33 Fig. 3

High- resolution electron microscopy and scanning electron microscopy measurements Typically HRSEM micrograph images. The images show uniform nanoparticle shape. The particles are well distributed with little agglomeration. x = 0 x = 0.1 x = 0.2 x = 0.3 x = 0.33 Fig. 4

Mössbauer Measurements At least two Ziman’s sextets related to Fe3+ ions on A-site and B-site, were used to fit the spectrum. An additional sextet was used to fit sample x = 0.1 By omitting Co from the sample x = 0.33, the spectrum shows super-paramagnetic behavior. no notes Fig. 4

Hyperfine Parameters Table 2 x δ (mm/s) H (kOe) Γ (mm/s) f (%) δA ±0.03 δB ±0.04 HA ±9 HB ±4 H3rd ±7 ΓA ±0.09 ΓB ±0.08 fA ±3 fB 0.31 453 485 - 0.32 0.24 50 0.1 0.30 0.34 473 493 439 0.26 0.21 41 24 0.2 442 480 0.42 0.17 49 51 0.3 419 467 0.55 70 30 0.33 0.38 161 409 0.94 1.35 47 53 Table 2

Magnetization Measurements Substituting cobalt by Mg, Sr and Mn atoms rapidly increase the magnetization from 32.79 emu/g to 76.61 emu/g for the x = 0 and x = 0.1 respectively, and then decreased to 32.87 emu/g for x = 0.33. Room Temperature Hysteresis loops can be understood in term of cations distribution. The coercivity decreases with increasing x value, as expected. Fig. 6

Magnetization Measurements Fig. 7

Low Temperature Measurements M-H curves in revealed a distortion (kink) at 2 K for the samples x = 0.1 and x = 0.2. The magnetization decreased dramatically as the temperature increases. The coercivity increases with decreasing temperature. Fig. 8

Low Temperature Measurements Fig. 9

Conclusions Glycol-thermal method was successfully used to synthesize single phase nanoferrites. Subsisting Co in sample x = 0.1, increased the magnetization up to 76.61 emu/g at room temperature. Reducing Co content weakness the super-interaction

Co-workers Dr T. Moyo Dr H. Abdallah

Acknowledgement South Africa National Research Foundation (NRF)

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